This invention relates to magnetic recording media, and more particularly, to magnetic recording media of metal thin film type, and a method for conducting recording/reproducing operation in such media.
Among magnetic recording media for use in video, audio and other applications, active research and development works have been made on magnetic recording media, usually magnetic tapes having a magnetic layer in the form of a continuous thin film because of the compactness of a roll of tape.
The preferred magnetic layers for such continuous metal film type media are deposited films of Co, Co--Ni, Co--O, Co--Ni--O and similar systems formed by the so-called oblique incidence evaporation process in which cobalt and optional elements are evaporated in vacuum-and directed at a given angle with respect to the normal to the substrate because such evaporated films exhibit superior characteristics. These media should have a flat surface because of remarkable deterioration of their properties due to a spacing loss. However, as the surface become flatter, the friction becomes greater adversely affecting head contact and transport movement.
Usually, the metal thin film type media have a magnetic layer as thin as 0.05 to 0.5 .mu.m so that the surface property of the media depends on the surface property of the substrate. For example, Japanese Patent Application Kokai No. 53-116115 discloses the provision of gently sloping protrusions in the form of creases or wrinkles on the substrate surface. Also, Japanese Patent Application Kokai Nos. 58-68227 and 58-100221 disclose the location of fine particles on the substrate surface, resulting in surface irregularities observable under an optical microscope with a magnifying power of 50 to 400 and actually measurable for height by means of a probe surface roughness meter. These media are, however, still insufficient in physical properties such as dynamic friction, runnability (the durability of tape which travels in frictional contact with rigid members in a recording machine), and moving stability as well as in electromagnetic properties.
Further, Japanese Patent Publication No. 39-25246 discloses the application of an organic lubricant on the surface of a ferromagnetic metal thin film layer as a topcoat layer for the purpose of reducing dynamic friction. The use of lubricant has the actually undesirable problem that it tends to adhere to the associated head to eventually block the head gap. At present, a technique for improving the surface properties of a metal thin film type magnetic recording medium has not been established which can reduce dynamic friction and eliminate head adhesion accompanied by head gap blocking without interfering smooth movement or adversely affecting electromagnetic properties.